RFR (XS): 8138684: G1 decision about taking regions into the collection set is too aggressive

[Thomas Schatzl]

Hi Jon,

On Thu, 2015-11-12 at 11:41 -0800, Jon Masamitsu wrote:
> 
> On 11/05/2015 02:49 AM, Thomas Schatzl wrote:
> > Hi all,
> >
[...]
> > So I thought of a formula that better represents the assumptions in the
> > GC code, and came up with this:
> >
> >   487   double safety_factor = (100.0 / G1ConfidencePercent) * (100 +
> > TargetPLABWastePct) / 100.0;
> >   488   size_t expected_bytes_to_copy = safety_factor * bytes_to_copy;
> >   489
> >   490   if (expected_bytes_to_copy > free_bytes) {
> 
> Thomas,
> 
> Change looks good.

Thanks for the review.

> 
> I would add a comment before the calculation of the safety factor.
> 
> // (100.0 / G1ConfidencePercent) represents a scale factor that
> // allows a more conservative calculation of the expected bytes
> // (i.e., a larger number expected bytes because there is always
> // uncertainty in predictions).
> // (100 + TargetPLABWastePct) / 100.0 represents the increase
> // in expected bytes due to anticipated waste in the PLAB's due
> // to unused space at the end of the evacuation.
> 
> If you find those accurate and helpful.

  I changed the comments to describe the factors.

Thanks,
  Thomas